Summary: In-Space Operations: Developing a Path to Affordable,
Evolutionary Space Exploration
David L. Akin
Space Systems Laboratory, University of Maryland, College Park, MD 20742
This paper explores alternative options for future human spaceflight programs which
meet the goals of the Vision for Space Exploration and the Augustine Commission, within
achievable cost and time limits. Based on four decades of NASA experience in on-orbit
operations, an architecture is developed that allows access throughout cislunar space, in-
cluding the surface of the Moon, through the use of multiple docking propulsion modules
to achieve the necessary mission V. The basic axiom of this study is that all Earth launch
must be accomplished solely with existing launch vehicles, to limit early budget require-
ments and minimize time between the start of the program and initial flight missions.
Analysis of prior spacecraft is used to estimate the feasibility of a human spacecraft with
a marginally smaller mass than the Apollo command module, which is capable of launch
via a direct translunar injection on a human-rated Delta IV Heavy. An optimized stan-
dard propulsion module, the Orbital Maneuvering Stage, is designed for lunar descent and
ascent, as well as multiple applications to in-space maneuvering. A modified version of
this vehicle, the Terminal Landing Stage, includes landing gear and required avionics for
the actual lunar landing. Along with dedicated costs to human-rate the Delta IV Heavy,
overall cost analysis was performed to find total program costs, and allow a year-by-year